Thorax:Arterial structure:Aorta
The aorta is the largest artery in the body, shuttling blood directly out of the left ventricle. The thoracic aorta has three parts - ascending, arch and descending. The ascending aorta begins at the aortic valve, located obliquely just to the left of the midline at the level of the third intercostal space. It courses anterosuperiorly and and terminates after exiting the fibrous pericarium and becomes the aortic arch behind the sternomanubrial joint (angle of louis). Branches: it normally has only two branches * The right coronary artery from the right aortic sinuses * The left coronary artery from the left aortic sinuses. The sinuses are outpouching of the aortic root each above a cusp of the aorta. The ascending aorta ascends slightly towards the right of midline where it can be seen as part of the mediastinal outline on a CXR. Relationships * Central location with respect to other vascular structures * Anterior to left atrium, posterior to right ventricle * Medial to right atrium and left ventricle The aortic arch is the continuation of the ascending aorta at the level of the sternomanubrial joint. It passes from right to left, front to back over the trachea and left bronchus. It terminate adjacent to the lower border of the T4 to become the descending aorta. Branches: * Brachiocephalic trunk: divides into right subclavian and right common carotid. It arises in or a little to the left of the midline of the body, ad slopes upwards across the trachea to the back of the right SC joint where it divides. * Left common carotid artery * Left subclavian artery * Ligamentum arteriosum ** Remnant of ductus arteriosus connecting superior aspect of pulmonary trunk to inferior aspect of aortic arch ** Connects pulmonary artery to aortic arch during embryonic/fetal circulation allowing blood to bypass lungs in utero; closes after birth Relationships: * Ascends anterior to right pulmonary artery and tracheal carina * Cross anteriorly by the phrenic nerve and vagus nerve (these are front and behind the lung root respectively). Between these lies the sympathetic and vagus branch of the superficial part of the cardiac plexus. * The left recurrent laryngeal nerve passes around the ligamentum arteriosum to pass upwards on the right side of the arch of the aorta. * Pulmonary trunk bifurcate in the concavity of the arch. * Oesophagus and trachea lies on the right side of the arch * Descends posterior to left hilum The descending aorta is the continuation of the aortic arch in the posterior mediastinum. It commences at the level of the T4 vertebra body, descends on left of midline and continues as the abdominal aorta at the aortic diaphragmatic hiatus at the level of the twelfth thoracic vertebra. Branches * Bronchial arteries, variable number, supply right and left main bronchi * Posterior intercostal arteries * Pericardial, esophageal, mediastinal, superior phrenic and subcostal branches Aortic Arch Variants * Bovine arch ** Left common carotid artery originating from brachiocephalic artery ** Most common great vessel anomaly, seen in up to 20% of population * Left brachiocephalic trunk * Aberrant right subclavian artery ** Seen in 0.4-2.3% of population, typically asymptomatic but may produce dyspnea/dysphagia ** Last aortic branch arising distal to left subclavian artery coursing cephalad, posteriorly and to the right, usually behind trachea and esophagus ** Diverticulum of Kommerell, focal dilatation of proximalaberrant subclavian artery, seen in 60% of cases * Anomalous origin: ** left vertebral artery: direct origin from aortic arch, seen in 10% of population ** thyroid ima artery * Right aortic arch ** Most common congenital arch anomaly (0.5-1%) ** Mirror image great vessel branching (Left brachiocephalic trunk, RCCA, RSCA) associated with congenital heart disease ** Non-mirror image great vessel branching, associated with aberrant left subclavian artery ** 70%: RCCA, LCCA, LSCA, RSCA ** 25%: Common stem for RCCA/LCCA, LSCA, RSCA ** 5%: Other variations with RSCA as last branch from AA * Double aortic arch ** Seen in 0.05-0.3% of population, usually symptoms of stridor/dysphagia, may be asymptomatic ** Most common complete vascular ring ** Right arch gives off right subclavian and right common carotid arteries *** Larger, extends more superiorly and posteriorly than left arch ** Left arch gives off left common carotid and left subclavian arteries * Aortic diverticulum of kummerell - dilated proximal descending aorta * Aortic nipple